Ultrafast Electron Transfer with Long-Lived Charge Separation and Spin Polarization in WSe2/C60 Heterojunction

The strong excitonic effect in monolayer transition-metal dichalcogenides (TMDs) endows them with intriguing optoelectronic properties but also short-lived population and valley polarization. Exciton dissociation by interfacial charge transfer has been shown as an effective approach to prolonging excited-state lifetimes. Herein, by ultrafast spectroscopy and building-block molecule C-60, we investigated exciton and valley polarization dynamics in the prototypical WSe2/C-60 inorganic-organic hybrid. We show that excitons in WSe2 can be dissociated through ultrafast (similar to 1 ps) electron transfer to C-60, with nanosecond charge separation due to thermally activated electron diffusion in C-60 film. Because of suppressed electron-hole exchange interaction after electron transfer, hole in WSe2 exhibits a spin/valley polarization lifetime of similar to 60 ps at room temperature, more than 2 orders of magnitude longer than that in WSe2 monolayer. This study suggests exciton dissociation as a general approach to suppress electron-hole interaction and prolong the charge/spin/valley lifetime in TMDs.

Automated summary

This study demonstrates that exciton dissociation can effectively suppress the electron-hole interaction in TMDs, thereby prolonging the charge/spin/valley lifetime.